This application is based upon and claims the benefit of priority from the prior Japanese Patent Applications No. 11-074122, filed Mar. 18, 1999; and No. 11-123792, filed Apr. 30, 1999, the entire contents of which are incorporated herein by reference.
The present invention relates to a cathode-ray tube, and more particularly, to a cathode-ray tube, in which a plurality of regions of a single phosphor screen are dividedly scanned by electron beams, and synthesizing images formed in the regions so as to produce one image.
In recent years, various discussions have been made on a high-resolution cathode-ray tube designed for high-definition broadcasting or having a large screen. For providing a cathode-ray tube with a high resolution, the diameter of a spot of an electron beam on the phosphor screen must be minimized. In contrast, the structures of electrodes constituting an electron gun have been improved or the electron gun itself has been remodeled to have a larger aperture or a larger length. However, no fruit has been born yet.
As the cathode-ray tube is made large in size, the distance from the electron gun to the phosphor screen becomes long, and the power of an electronic lens becomes too high. This is the most critical reason why no fruit has been born yet. Consequently, for realizing a high resolution, the distance from the electron gun to the phosphor screen (depth) must be decreased. At this time, if an electron beam is deflected at a wide angle, a difference in magnification between the center of the screen and the periphery thereof increases. This is therefore unacceptable in terms of the high resolution.
According to a conventionally adopted method, a plurality of electron guns and a plurality of deflection yokes are employed in order to dividedly scan a plurality of regions defined of a single phosphor screen. Images rendered in the regions are joined to produce a large image. For example, Jpn. Pat. Appln. KOKAI Publication Nos. 7-45215 and 2-51831 have disclosed cathode-ray tubes for joining two images to produce a large picture. Moreover, Japanese Unexamined Patent Publications Nos. 61-256552 and 61-256551 have proposed cathode-ray tubes for joining a larger number of images to produce a large picture.
This kind of cathode-ray tube has a vacuum envelope having a panel, a funnel including two corn portions and coupled to the panel, and two necks coupled to the funnel. A deflection unit is mounted on the external surface of each corn portion. An electron gun is arranged in each neck.
In the cathode-ray tube having the above components, electron beams emitted from the electron gun are deflected due to magnetic fields generated by the deflection units. A phosphor screen formed on the inner surface of the panel has two regions corresponding to the electron guns and the two regions are dividedly scanned by the electron beams. Sub-images rendered on the phosphor screen are joined by controlling signals to be applied to the electron guns and deflection units. Consequently, one large image having neither a break nor overlap is produced over the whole surface of the phosphor screen.
As mentioned above, the cathode-ray tube uses the electron beams emitted from the plurality of electron guns to dividedly scan a plurality of regions on the phosphor screen. For producing an image that has neither a break nor an overlap created on a boundary between adjoining scanning regions, a shadow mask must be highly precisely arranged and held at a predetermined position relative to the phosphor screen. Specifically, the phosphor screen and the electron beam passage apertures of the adjoining shadow mask must have a predetermined positional relationship.
In the cathode-ray tube having the above components, the relative positions between the shadow mask and the panel are determined in the course of manufacturing and greatly dependent on precision in assembling.
Even in a typical picture tube, if a pitch between phosphor dots in the phosphor screen or the width of a phosphor dot is different from a predetermined value by several ten xcexcm, the difference is discernible. The precision in assembling the shadow mask and panel must be higher than several ten xcexcm in the above-mentioned cathode-ray tube.
The precision in assembling the shadow mask and panel of a typical picture tube is about several hundred xcexcm. In the case of the aforesaid dividedly scanning cathode-ray tube, as long as the same assembling procedure is adopted, it is hard to produce an image that is seen continuously with the boundary between adjoining sub-images indiscernible.
Moreover, the precision in a single component such as the shadow mask or panel has a significant meaning. Specifically, a difference in the precision of a produced shadow mask included in a typical picture tube, that is, a difference of any dimension of a produced shadow mask from a design value is about several hundred xcexcm. Moreover, a difference in the precision of an inner surface of a produced panel, that is, a difference of any dimension of the inner surface from a design value is also about several hundred xcexcm. When the difference is taken into consideration, if a dividedly scanning cathode-ray tube is produced according to a conventional configuration and a conventional assembling procedure, it is quite hard to attain desired precision in terms of the boundary between sub-images.
Moreover, a shadow mask may be thermally expanded with the impact of electron beams or may be vibrated with extraneous vibrations and howled. In this case, the relative positions of the shadow mask and phosphor screen are changed, and an electron beam is landed incorrectly. This leads to deterioration in image definition. In particular, as far as a dividedly scanning cathode-ray tube is concerned, an electron beam is likely to be landed incorrectly on the boundary portion between the scanning regions of the phosphor screen. It is hard to provide an image with continuity.
The present invention has been contrived in consideration of the above circumstances, and its object is to provide a cathode-ray tube in which a shadow mask and an inner surface of a panel are positioned and held with a desired positional relationship established, and which can be readily produced according to a conventional manufacturing process.
For accomplishing the above object, a cathode-ray tube according to the present invention comprises a vacuum envelope including a panel that has a phosphor screen formed on an inner surface thereof; a plurality of electron guns disposed in the vacuum envelope, for emitting electron beams to the phosphor screen and dividedly scanning a plurality of scanning regions on the phosphor screen; a shadow mask arranged between the phosphor screen and the electron guns and the having a plurality of effective areas which include numerous electron beam passage apertures and are defined in association with the scanning regions, and a boundary portion defined between the effective areas and opposing to the boundary between the scanning regions of the phosphor screen; and a coupling member coupled to the boundary portion of the shadow mask in order to hold the boundary portion at a predetermined position.
With the cathode-ray tube having the above construction, the boundary portion of the shadow mask is held at the predetermined position by means of the coupling member. When the shadow mask is thermally expanded or subjected to extraneous vibrations, the coupling member works to restrain displacement of the shadow mask. The shadow mask and phosphor screen can be held at predetermined relative positions, thereby suppressing incorrect landing of electron beams on the boundary portion of the shadow mask which is attributable to a change in the gap (q value) between the inner surface of the panel and the shadow mask. Sub-images rendered on the plurality of scanning regions can be joined continuously without a break or overlap. This leads to improved image definition.
Moreover, a cathode-ray tube according to the present invention comprises a vacuum envelope including a panel that has a phosphor screen formed on an inner surface thereof; a plurality of electron guns disposed in the vacuum envelope, for emitting electron beams to the phosphor screen and dividedly scanning a plurality of scanning regions on the phosphor screen; a shadow mask arranged between the phosphor screen and the electron guns and the having a plurality of effective areas which include numerous electron beam passage apertures and are defined in association with the scanning regions, and a boundary portion defined between the effective areas and opposing to the boundary between the scanning regions of the phosphor screen; and a position adjustment mechanism used to adjust the gap between the inner surface of the panel and the shadow mask at a plurality of positions on the boundary portion of the shadow mask.
According to the cathode-ray tube having the foregoing construction, the position adjustment mechanism is provided for adjusting the gap (q value) between the inner surface of the panel and the shadow mask at the plurality of points on the boundary portion of the shadow mask. The q value can therefore be adjusted at a step preceding the step of assembling the components of the vacuum envelope. A difference of the q value from a predetermined value is attributable to a difference in precision in assembling the panel and shadow mask. The difference in precision in assembling the panel and shadow mask may attribute to a difference in precision in working a shadow mask and a different in precision in producing the inner surface of a panel. The difference of the q value is adjusted at the plurality of points on the boundary portion and thus corrected. The q value can therefore be set accurately to the predetermined value over the whole boundary portion.
Consequently, when the phosphor screen is exposed to light, phosphor layers can be formed continuously along the boundary between the scanning regions. When the cathode-ray tube is in operation, the plurality of scanning regions can be scanned accurately. Consequently, an image having neither a break nor overlap created on the boundary between the scanning regions can be displayed.
Furthermore, in the cathode-ray tube according to the present invention, the shadow mask includes a mask body in which electron beam passage apertures are bored and a mask frame attached to the periphery of the mask body. The position adjustment mechanism includes an adjustment member fixed to the mask body. After the adjustment member is used to adjust the q value, the adjustment member is fixed to the mask frame. Even when the shadow mask is thermally expanded or subjected to extraneous vibrations, the adjustment member is used to restrain displacement of the shadow mask. The shadow mask and phosphor screen can be held at the predetermined relative positions. Consequently, incorrect landing of an electron beam attributable to a change in the q value can be minimized, and image definition can be improved.
Another cathode-ray tube according to the present invention comprises a vacuum envelope including a panel that has a phosphor screen formed on an inner surface thereof; a shadow mask arranged in the vacuum envelope and opposing the phosphor screen; and a plurality of electron guns incorporated in the vacuum envelope, for emitting electron beams to the phosphor screen via the shadow mask, and dividedly scanning a plurality of scanning regions on the phosphor screen. The shadow mask includes a mask body having a plurality of effective areas in which numerous electron beam passage apertures are bored and a boundary portion defined between the effective areas and opposed to the boundary between the scanning regions of the phosphor screen, and a substantially rectangular mask frame holding the periphery of the mask body; and the mask frame includes a pair of long-side walls and a middle frame extending between the pair of long-side walls and opposing the boundary portion of the mask body.
According to the present invention, the shadow mask has a coupling member coupled to the boundary portion on the inner surface of the mask body in order to hold the boundary portion at a predetermined position.
Furthermore, in the color cathode-ray tube according to the present invention, the coupling member is fixed to the middle frame of the mask frame.
With the color cathode-ray tube having the foregoing construction, the mask frame has the middle frame. The shadow mask therefore exhibits improved rigidity. The mask body can be held at the predetermined position highly precisely on a stable basis. Moreover, the coupling member used to adjust the gap between the mask body and the inner surface of the panel is coupled to the mask body and fixed to the middle frame of the mask frame. The mask body can therefore be secured and held more precisely. The strength of the whole shadow mask improves. The shadow mask can be attached or detached to or from the panel as it is conventionally. Moreover, the color cathode-ray tube can be produced without the necessity of drastically modifying a conventional manufacturing process.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.